Behavioral manifestations resulting from interactions between different neurotransmitter systems have been observed in clinical practice (e.g., extrapyramidal side effects secondary to administration of neuroleptics) and interactions have been demonstrated physiologically, in animal studies. It is clear that specific neurotransmitter systems do not work in isolation and that behavior results from synergistic responses between neurochemically different systems. It has only recently become possible to measure neurotransmitter activity and interactions in vivo in non-human-primates and humans due to advances in neuroimaging and radiochemistry. The experimental approach will be to relate PET studies using 18f-altranserin, a dopamine D2 agonist and 50 water to measure regional blood flow to prolactin response to flenfluramine in normal subjects.